Just C&P’ing, but here’s what I found on the 6.5L-T Manifold bolts/studs:
These are M10-1.5 with a non-std, semi-locking thread.
Qty: 5 of P/N: 10137539 stud 85mm long.
Qty: 9 of P/N: 14028922 65mm long.
Qty: 4 of P/N: 14928923 45mm long.
And the Tq is less than the other M10’s used on the engine – something like 16-18Ft/Lbs do to the locking thread feature.
If your worried about them being rusted in, I wouldn’t even touch them unless you have/use a >400Ft/Lbs ½” drive impact gun! If you use a breaker bar you run the risk snapping them off in the head (at which point you just screwed the pooch) as I believe these are rated at or above 10.9/12.9, IE quite hard to drill out!